vmm: Clean Error handling up

We used to have errors definitions spread across vmm, vm, api,
and http.

We now have a cleaner separation: All API routines only return an
ApiResult. All VM operations, including the VMM wrappers, return a
VmResult. This makes it easier to carry errors up to the HTTP caller.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vmm/src/vm.rs

@@ -209,6 +209,12 @@ pub enum Error {
 
     /// Failed to create a new KVM instance
     KvmNew(io::Error),
+
+    /// VM is not created
+    VmNotCreated,
+
+    /// Cannot clone EventFd.
+    EventFdClone(io::Error),
 }
 pub type Result<T> = result::Result<T, Error>;